Effects of internal fluctuations on the spreading of Hantavirus

We study the spread of Hantavirus over a host population of deer mice using a population dynamics model. We show that taking into account the internal fluctuations in the mouse population due to its discrete character strongly alters the behaviour of the system. In addition to the familiar transition present in the deterministic model, the inclusion of internal fluctuations leads to the emergence of an additional deterministically hidden transition. We determine parameter values that lead to maximal propagation of the disease, and discuss some implications for disease prevention policies

Biodegradation and biological treatments of cellulose, hemicellulose and lignin: an overview

In nature, cellulose, lignocellulose and lignin are major sources of plant biomass; therefore, their recycling is indispensable for the carbon cycle. Each polymer is degraded by a variety of microorganisms which produce a battery of enzymes that work synergically. In the near future, processes that use lignocellulolytic enzymes or are based on microorganisms could lead to new, environmentally friendly technologies. This study reviews recent advances in the various biological treatments that can turn these three lignicellulose biopolymers into alternative fuels. In addition, biotechnological innovations based on natural delignification and applied to pulp and paper manufacture are also outlined

Mesophilic anaerobic co-digestion of the organic fraction of municipal solid waste with the liquid fraction from hydrothermal carbonization of sewage sludge

In the present study, the influence of substrate pre-treatment (grinding and sieving) on batch anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was first assessed, then followed by co-digestion experiments with the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered sewage sludge (DSS). The methane yield of batch anaerobic digestion after grinding and sieving (20 mm diameter) the OFMSW was considerably higher (453 mL CH4 STP g−1 VSadded) than that of untreated OFMSW (285 mL CH4 STP g−1 VSadded). The modified Gompertz model adequately predicted process performance. The maximum methane production rate, Rm, for ground and sieved OFMSW was 2.4 times higher than that of untreated OFMSW. The anaerobic co-digestion of different mixtures of OFMSW and LFHTC of DSS did not increase the methane yield above that of the anaerobic digestion of OFMSW alone, and no synergistic effects were observed. However, the co-digestion of both wastes at a ratio of 75% OFMSW-25% LFHTC provides a practical waste management option. The experimental results were adequately fitted to a first-order kinetic model showing a kinetic constant virtually independent of the percentage of LFHTC (0.52–0.56 d−1) and decreasing slightly for 100% LFHTC (0.44 d−1)The authors wish to express their gratitude to the Spanish MINECO (CTM2016-76564-R) for providing financial support. M. A. de la Rubia received financial support from the Spanish Ministry of Economy and Competitiveness (RYC-2013-12549

Anaerobic co-digestion of the aqueous phase from hydrothermally treated waste activated sludge with primary sewage sludge. A kinetic study

The mesophilic anaerobic co-digestion of the liquid fraction from hydrothermal carbonization (LFHTC) of dewatered waste activated sludge with primary sewage sludge (PSS) has been studied. Mixtures of different composition (25, 50 and 75% of LFHTC on a chemical oxygen demand (COD) basis), as well as the individual substrates, have been tested using two inocula (flocculent (FS) and granular (GS) sludges). Methane production decreased as the LFHTC/PSS ratio increased, which can be related to the presence of recalcitrant compounds in the LFHTC, such as alkenes, phenolics, and other oxygen- and nitrogen-bearing aromatics hard-to-degrade through anaerobic digestion. Methane yield reached 248 ± 11 mL CH4 STP/g CODadded with the GS inoculum and 25% LFHTC. A 74 and a 30% increase of methane production was achieved in the 25% LFHTC runs respect to the obtained in the similar experiments with 100% LFHTC, using the FS and GS inocula, respectively. In those late runs, the COD was reduced more than 86%, with a negligible concentration of total volatile fatty acids. With both inocula, total Kjeldahl nitrogen hydrolysis increased as the LFHTC to PSS mixture ratio decreased, reaching values higher than 79% at the end of the experiments. Methane yield values fitted well the first-order, Cone and Weibull kinetic models for both inocula. Significant differences in the kinetic constant values, ranging from 0.100 to 0.168 d−1 and 0.059–0.068 d−1, were found with the FS and GS inocula, respectively. The results obtained support the potential integration of HTC of dewatered waste activated sludge in wastewater treatment plantsThe authors greatly appreciate financial support from the SpanishMINECO (Project CTM2016-76564-R) and the Community of Madrid(Project P2013/MAE-2716). M.A. de la Rubia acknowledges financialsupport from the Spanish MINECO (RYC-2013-12549). The valuablecontribution of

Anaerobic co-digestion of the process water from waste activated sludge hydrothermally treated with primary sewage sludge. A new approach for sewage sludge management

Hydrothermal carbonization (HTC) is a suitable technology for managing wastes with a high moisture content, providing a carbon-rich and high energy density material called hydrochar and a process water (PW) with significant organic matter content. The aim of this work was to develop a new approach to sewage sludge management involving anaerobic digestion (AD) of the PW of dewatered waste activated sludge (DWAS) with primary sewage sludge (PSS). The process was optimized by performing semi-continuous experiments with different feed mixture compositions (10% PW/90% PSS and 5% PW/95% PSS, on a COD basis), organic loading rates (OLR; 1.5 and 2.5 g COD L−1 d−1), and temperature regimes (mesophilic and thermophilic). The combination of mesophilic conditions, a 10% PW/90% PSS feed mixture and OLR of 1.5 g COD L−1 d−1 provided concentrations of volatile fatty acids <400 mg COD L−1 in addition to a methane yield (172 ± 11 mL CH4 g−1 CODadded), 1.15 times the value for the control test (100% PSS). Therefore, the energy content of hydrochar from HTC of DWAS followed by AD of the process water with primary sewage sludge enhances the valorization of this renewable residueThe authors greatly appreciate funding from Spain's MINECO (Project CTM2016-76564-R; project RYC-2013-12549), Madrid Regional Government (Project P2018/EMT-4344) and UAMSantander (Project 2017/EEUU/07

Valorization of microalgal biomass by hydrothermal carbonization and anaerobic digestion

The potential of hydrothermal carbonization (HTC) as a novel choice for treating microalgal biomass (MAB) was assessed. The hydrochar obtained at 210 °C had a carbon content and a higher heating value (HHV) 1.09 and 1.1 times greater, respectively, than that of the feedstock. Also, washing the hydrochar with HCl efficiently removed ash and increased its carbon content 1.40-fold. Energy recovery in the liquid fraction from the hydrothermal treatment (LF) by anaerobic digestion (AD) allowed methane yields of 188–356 mL STP CH4 g−1 VSadded, to be obtained. As a result, the amount of energy recovered from MAB was increased from about 4 MJ kg−1 (20% in terms of HHV) to 15.4, 12.1 and 10.4 MJ kg−1 by combining HTC at 180, 210 and 240 °C, respectively, with AD. Therefore, HTC at 180 °C in combination with AD seemingly provides an effective method for valorizing MABThe authors wish to express their gratitude to Spain’s MINECO (CTM2016-76564-R and 449 RYC-2013-12549) for funding this wor